The school psychologist was researching the results of a third school and found them to closely fit a normal distribution with a mean completion time of 20.68 minutes and a standard deviation of 5.3 minutes. Unfortuantly, after he had finished calculating the results, he could not read of of the observed values. Given there are 125students at the school, and a percentage error of ten percent determine the possible range of values for the observed frequencies, falling between 14.5 and the 19.5 minute interval. Equations: z(standardised score) = (x-mean/standard dev) Percentage error = |o-e|/total frequency * 100. I have no clue.. please help me!